Research Updates

Co-chaired by three members of CAF’s Research Consortium—Drs. David Holtzman, Sam Sisodia and Rudy Tanzi—participants included all the other members of the Research Consortium (except Virginia Lee, who had a prior commitment) and several invited guests whose records of research include valuable insights into this relationship. The guests were Michael Brown, MD, and Joachim Herz, MD, Southwestern Medical School; Alan Tall, MD, Columbia University; Karl Weisgraber, Ph.D., Gladstone Institute, University of California, San Francisco; and Cheryl Wellington, Ph.D., University of British Columbia.

The Amyloid-beta protein is a key contributor to Alzheimer’s pathology and the prevailing theory has been that Abeta has no function other than as a waste product created by the brain. It is acknowledged by most researchers to be a key “bad guy” in Alzheimer’s pathology.

A spate of headlines recently dimmed hopes for a wonder drug to fight Alzheimer’s disease. We know the existing drugs used to treat Alzheimer’s patients, including Aricept, Namenda and others, provide only modest symptomatic relief but do not treat the root pathology of the disease. Let’s look at three new drugs that attempted to get at the causes of the disease but failed. We’ll look at the “bad news,” comment on why they failed and then look at what’s in the pipeline signaling better news.

Chronic sleep deprivation in mice with Alzheimer’s disease-type changes makes Alzheimer’s brain plaques appear earlier and more often, researchers led by Cure Alzheimer’s Fund’s Dr. David M. Holtzman at Washington University School of Medicine in St. Louis reported in Science Express. The study was funded in part by Cure Alzheimer’s Fund.

They also found that orexin, a protein that helps regulate the sleep cycle, appears to be directly involved in the increase. Neurodegenerative disorders like Alzheimer's disease and Parkinson's disease often disrupt sleep. The new findings are some of the first indications that sleep loss could play a role in the genesis of such disorders.

"Orexin or compounds it interacts with may become new drug targets for treatment of Alzheimer's disease," says senior author Holtzman, the Andrew and Gretchen Jones Professor and chair of the Department of Neurology at the School of Medicine, and neurologist-in-chief at Barnes-Jewish Hospital. "The results also suggest that we may need to prioritize treating sleep disorders not only for their many acute effects, but also for potential long-term impacts on brain health."

Holtzman's laboratory uses a technique called in vivo microdialysis to monitor levels of amyloid beta in the brains of mice genetically engineered as a model of Alzheimer's disease. Amyloid beta is a protein fragment that is the principal component of Alzheimer's plaques.

Jae-Eun Kang, Ph.D., a post-doctoral fellow in Holtzman's lab, noticed that brain amyloid beta levels in mice rose and fell in association with sleep and wakefulness, increasing in the night, when mice are mostly awake, and decreasing during the day, when they are mostly asleep.

A separate study of amyloid beta levels in human cerebrospinal fluid led by Randall Bateman. M.D., assistant professor of neurology and a neurologist at Barnes-Jewish Hospital, also showed that amyloid beta levels were generally higher when subjects were awake and lower when they slept.

To confirm the link, Kang learned to use electroencephalography (EEG) on the mice at the Sleep and Circadian Neurobiology Laboratory at Stanford University with researchers Seiji Nishino, M.D., Ph.D., and Nobuhiro Fujiki, M.D. Ph.D. The EEG readings let researchers more definitively determine when mice were asleep or awake and validated the connection: Mice that stayed awake longer had higher amyloid beta levels.

"This makes sense in light of an earlier study in our lab where John Cirrito, Ph.D., showed that increases in synaptic activity resulted in increased levels of amyloid beta," Holtzman notes. "The brain's synapses may generally be more active when we're awake."

Depriving the mice of sleep caused a 25 percent increase in amyloid beta levels. Levels were lower when mice were allowed to sleep. Blocking a hormone previously linked to stress and amyloid beta production had no effect on these changes, suggesting they weren't caused by the stress of sleep deprivation, according to Holtzman.

Researchers elsewhere had linked mutations in orexin to narcolepsy, a disorder characterized by excessive daytime sleepiness. The brain has two kinds of receptors for orexin, which also is associated with regulation of feeding behavior.

When Holtzman's group injected orexin into the brains of the mice, mice stayed awake longer and amyloid beta levels increased. When researchers used a drug called almorexant to block both orexin receptors, amyloid beta levels were significantly lower and animals were awake less.

Miranda M. Lim, M.D., Ph.D., a neurology resident and post-doctoral researcher in Holtzman's lab, performed long-term behavioral experiments with the mice. She found that three weeks of chronic sleep deprivation accelerated amyloid plaque deposition in the brain. In contrast, when mice were given almorexant for two months, plaque deposition significantly decreased, dropping by more than 80 percent in some brain regions.

"This suggests the possibility that a treatment like this could be tested to see if it could delay the onset of Alzheimer's disease," says Holtzman.

Holtzman notes that not only does the risk of Alzheimer's increase with age, the sleep/wake cycle also starts to break down, with older adults progressively getting less and less sleep. Investigators are considering epidemiological studies of whether chronic sleep loss in young and middle-aged adults increases risk of Alzheimer's disease later in life. Holtzman also plans to learn more of the molecular details of how orexin affects amyloid beta.

"We would like to know if there are ways to alter orexin signaling and its effects on amyloid beta without necessarily modifying sleep," he says.

Additional studies will address the questions of whether increased amyloid beta during wakefulness is connected to increased synaptic activity and whether some aspect of sleep lowers amyloid beta levels independent of synaptic activity.

Vaccination against amyloid is a promising approach for the development of Alzheimer’s disease (AD) therapeutics. Approximately half of the investigational new therapeutics in human clinical trials for AD are active or passive immunotherapeutics.

Active vaccination involves the injection of an antigen and relies on the production of antibodies in the vaccinated patient. Four human clinical trials of active vaccination currently are under way. Passive immunization is also a promising strategy that involves the production of antibodies outside of the patient and injection of these antibodies. There are currently 12 clinical trials of passive immunization. You can check for Alzheimer therapeutics in human clinical trials by visiting www.clinicaltrials.gov and searching for key words “Alzheimer’s and immunotherapy.”

Thinking out of the box

The development of vaccinations as a strategy for treating or preventing Alzheimer’s is an example of thinking out of the box. Vaccinations commonly are associated with infectious diseases, like influenza, small pox and polio, which appear to have little in common with neurodegenerative diseases, like Alzheimer’s. Moreover, the brain is an immunoprivileged site with little access to antibodies, so it seems unlikely antibodies would be protective in the brain.

Researchers were pleasantly surprised when Dale Schenk and co-workers at Elan Inc. reported that vaccination of transgenic mouse models of AD against the amyloid Aß peptide prevented amyloid deposition in young animals and removed pre-existing amyloid deposits in older animals. Subsequent work showed that immunization against Aß prevented or reversed many other pathological features and prevented cognitive dysfunction in transgenic mice and non-human primates. This vaccine (Elan AN1792) was tested in human clinical trials, where it showed similar beneficial effects of removing amyloid deposits and slowing cognitive decline in patients with significant levels of anti-Aß antibodies, but the clinical trial was halted because 6 percent of the patients developed meningoencephalitis, an inflammatory side effect.

Second-generation vaccines and passive immunization

To circumvent the unwanted inflammatory side effects, second-generation active vaccines have been developed and passive immunization strategies have been explored. The second-generation vaccines use small pieces of the amyloid Aß sequence to avoid activating the T-cells responsible for meningoencephalitis, while passive immunization bypasses the human immune response by directly supplying antibodies. These newer strategies have shown the same beneficial effects in transgenic mice and passive immunization has shown some promise in a subset of patients in human trials, but they have raised new questions about their effectiveness and potential new side effects. Elan/Wyeth reported preliminary results from clinical trials of their monoclonal antibody, Bapineuzimab, that demonstrated only a small benefit in a subgroup of patients who lack the apoE4 genotype. They also failed to observe an improved benefit with an increased dose of antibody and reported side effects, like a buildup of fluid in the brain. Results of active vaccination human clinical trials with second-generation vaccines remain to be reported.

Third-generation vaccines and antibodies: Thinking perpendicular to the box

Both second-generation vaccines and antibodies suffer from a common problem. They both target linear amino acid sequences found in normal human proteins (the amyloid precursor protein) and in the amyloid deposits themselves. Making antibodies against normal human proteins can cause autoimmune side effects, in which the immune system is attacking normal human cells in addition to the Alzheimer’s pathology. Fortunately, it is difficult to make antibodies against self-proteins because of immune suppression of auto antibodies. Third-generation vaccines seek to overcome these problems of autoimmune side effects and autoimmune suppression by using antibodies that target structures specific to the amyloid aggregates and that do not react with normal human proteins.

Cure Alzheimer’s Fund has been supporting two projects that seek to develop third-generation immunotherapeutics. Dr. Charles Glabe’s laboratory is developing active vaccines and monoclonal antibodies that recognize conformations of the amyloid peptide that only occur in the pathological amyloid oligomer aggregates, while Dr. Rob Moir’s lab is working on cross-linked amyloid peptides (CAPs) that are only found in disease-related aggregates. Dr. Glabe’s strategy relies on the fact that when the Aß peptide aggregates into ß-sheet oligomers, it creates new antibody recognition sites, known as epitopes, that are not found on native proteins. The surprising finding is that these oligomer-specific antibodies recognize amyloid oligomers from other diseases that involve amyloids formed from sequences unrelated to Aß. This means the same antibodies also may be effective for other amyloid-related neurodegenerative diseases, like Parkinson’s disease.

The explanation for why the antibodies are specific for amyloid oligomers that involve several individual peptide strands arranged in a sheet and yet recognize these sheets when they are formed from other amino acid sequences is simple and elegant (Figure 1). It is now known that most pathological amyloids aggregate into simple and very regular structures where the peptide strands are arranged in parallel and where the amino acid sequence is in exact register. This is like a sheet of paper upon which the same sentence is written on each line. The individual amino acids line up and down the sheet in homogeneous tracts, known as “steric zippers.” The steric zippers do not occur in normal protein structures and the oligomer-specific antibodies are thought to recognize these steric zipper patterns on the surface of the sheets. Since all proteins are made up using the same 20 amino acids, any sequence in this parallel, in-register structure gives rise to the same steric zippers regardless of the linear sequence, which can explain why the antibodies recognize the oligomers formed by different proteins.

Dr. Moir’s group is working on CAPs, where Aß is cross-linked by oxidation of a tyrosine residue at position 10 of the peptides’ sequence. Aß is oxidized after it is produced from the amyloid precursor protein as a consequence of the abnormally high level of oxidative activity in a brain with AD and the peptides’ propensity to bind redox active metals. Excessive CAPs generation is associated with the disease state and is not a normal feature of Aß biology. The cross-linking at tyrosine 10 that gives rise to CAPs may serve to align the peptides in a parallel, in-register fashion and promote the generation of still-larger oligomeric aggregates that display steric zippers on their surface.

Dr. Moir and Dr. Rudy Tanzi’s labs found that natural antibodies to CAPs are reduced in the blood of patients with AD. More recently, evidence published by Tony Weiss-Coray’s group at Stanford University supports the idea that antibodies that recognize steric zippers and CAPs may be important for protecting against Alzheimer’s disease. The levels of these antibodies that target the zippers and CAPs were among the highest in young, normal humans; levels dropped with aging and with AD. Furthermore, the results of a recent study supported by Baxter Biosciences of patients that received human antibodies purified from normal individuals (IVIg) reported that antibody treatment reduced the risk of being diagnosed with AD by 42 percent over the five-year study period. This is one of the most remarkable reports of prevention of AD by any therapy. Although the normal human antibodies that target amyloid primarily recognize the steric zippers and CAPs, these antibodies are present at relatively low levels. It is reasonable to imagine that an even greater protective effect might be achieved by boosting the levels of these protective antibodies by either active vaccination or passive immunization.

Figure 1 shows how the same steric zipper patterns are formed on parallel, in-register oligomers from completely different sequences. A segment of the Aß sequences is shown in the upper left corner and a random sequence is shown in the upper right. Each amino acid is designated by a capital letter. Typical antibodies recognize the linear sequence (from left to right) indicated in the horizontal boxes, which is unique to each sequence. When the peptides aggregate to form pathological oligomers, they line up in a parallel, in-register fashion, shown below. This gives rise to steric zippers that run up and down the sheet perpendicular to the sequence, shown in vertical boxes. Aggregation-dependent, disease-specific antibodies recognize the steric zippers from many different amyloid sequences. Zippers from F and V amino acids are shown in boxes, but there are potentially 20 different zippers; one for each of the 20 amino acids.

The fact that a completely random sequence can form the same type of steric zipper as is found in Aß amyloid in Alzheimer’s disease means we can use a non-human, random peptide sequence as a vaccine to produce a protective immune response that has a very low potential for autoimmune side effects. Vaccines based on non-human peptides, like diphtheria and pertussis toxin, are so safe they routinely are given to infants. There is no reason to expect that a vaccine for AD that targets the disease-specific steric zippers wouldn’t be as safe and free of side effects. A goal of the research funded by Cure Alzheimer’s Fund is to do the preclinical investigations that are a necessary prelude to getting these third-generation vaccines and monoclonal antibodies that target disease-specific epitopes into human clinical trials.

This Science Update gives you an overview about what is know about the science behind Alzheimer’s disease and how at Cure Alzheimer's Fund we are funding research to get to a cure as quickly as possible.

Research Update

There has been a spate of announcements about promising drug therapies, “new” genes and environmental factors affecting Alzheimer’s disease (AD) in the news lately. These are likely to increase as the media becomes more sensitized to the looming disaster that Alzheimer’s presents to the world.

We thought it would be useful to bring you up to date on our research agenda. Cure Alzheimer's Fund’s supported research is active in basic genetic research and early stages of drug development, and also addresses several key environmental factors.

From an article in Medical News Today about a paper recently released in the journal Neuron, June 7, 2007:

Researchers from the MassGeneral Institute for Neurodegenerative Disorders (MGH-MIND) have discovered how brain cells affected by stroke or head injury may cause generation of amyloid-beta protein, which is a key factor in the Alzheimer’s disease story.